Unlock... Flash... spts... OMG

[kodabb]

hi and hello!
i've just joined this community because i saw that many people really helped and solved other people's problems!
Right now i'm a complete newby in flashing or unlocking, but i hope that you'll help me all the same!
I've tried to look for a tutorial or something like that, but i can't find anything anyway...

First thing i'm trying to understand is: what is the difference between Unlocking and Flashing?
i saw that there are many unlockers as well as many flasher but i really can't tell them apart!

For example, i have a sharp gx 17: i'd like to remove the Vodafone theme, change the right button link and enable the Bluetooth for receiving files from others mobile phones...
should i use an unlocker or a flasher?

another thing: i saw that there are many different firmware... but what exaclty is? is it just a phone file system? or something different? does it have something to do with the spts stuff (what is that btw?)?

i think that these two questions are enough... for now

thanks a lot guys!!!
Koda